The big picture: Plants evolved from green algae
- Cyanobacteria & protist made landfall ~1.2 bya
- plants, fungi and animals ~500 mya
- first forests 385 mya
- Plants evolved from green algae
- Several key ‘shared traits’
- WHAT DO YOU THINK THEY ARE?
- Plants support all life on earth
- Oxygen to breath
- food to eat
- new habitats

Green Algae (Oedogonium)
- Sister group to land plants
- marine and freshwater
- single and multi-cellular
- broad, thick filaments
- some have AoG
- evolved around ~750mya
- Reproductive features:
- Oogonia = egg containing cell
- Antheridium = sperm containing cell


Molecular evidence points at charophytes as plant ancestors


Charophytes (freshwater green algae)
- Transition from water to land starts with Charophytes
- freshwater habitats may have dried
- a population eventually lived above water line
- More shared traits with land plants:
- circular protein rings in plasma membrane; make cellulose fibers in cell wall
- swimming sperm with similar structure


Land plants are a monophyletic group

All land plants are embryophytes

- 10 divisions of land plants
- Zygote develops into multicellular embyro, while enclosed in reproductive structure
- algae do not retain embryo
- Land plant & embryophyte terms used interchangeably
Multi-cellular, Dependent embryos (placental transfer)

Shared Traits further define plant evolution


Waxy cuticle and stomata

Multi-cellular Gametangia

Photosynthesis with unique pigments (chlorophyll A & B)

Unique cell walls
- Cells walls made of cellulose
- Pectin to fortify cell walls
- Produce cells walls in unique way

Alternation of generations

- Land plants alterate between diplod (2N) and haploid (1N) generations
- diploid = sporophyte
- haploid = gametophyte
- sex cells (1N) make zygote (2N)
- zygote → embryo → sporophyte (all mitosis)
- sporophyte makes spores (1N) by meosis
- spores germinate into gametophyte (1N) by mitosis
- gametophyte makes sex cells (sperm and egg)
- dominance of different generations key for evolution
First plant group: non-vascular bryophytes (mosses)
- Mosses, hornworts and liverworts
- Fossils of bryophyte spores ~470mya
- Non-vascular; ground hugging carpets
- bodies to thin to support height growth
- Have a rhizoid but not a root
- anchors plant
- does not uptake water


Bryophytes have gametophyte dominated life cycle
